Rare Earth Ion Implantation in GaN: Damage Formation and Recovery

Abstract

Rare earth ions implanted GaN has been investigated by transmission electron microscopy versus the fluence, using Er, Eu or Tm ions at 150 keV or 300 keV and at room temperature. Point defect clusters and stacking faults are generated from low fluences (7 × 10 13 at/cm 2 ), their density increases with the fluence up to the formation of a highly disordered layer at the surface. This highly disordered layer is observed from a threshold fluence of 3×10 14 at/cm 2 at 150 keV and 3×10 15 at/cm 2 at 300 keV, and appears to be composed of voids and misoriented nanocrystallites. Its thickness rapidly increases with the fluence, and then saturates. Both basal and prismatic stacking faults were observed. Basal stacking faults are I 1 in majority, but E or I2 have also been identified. I1 basal stacking faults propagate easily through GaN by folding from basal to prismatic planes. Channelling implantation, increasing the implantation temperature from room temperature to 500 • C, or implanting through a 10 nm thick AlN cap reduce the crystallographic damage, particularly by retarding the formation of the highly disordered layer. Implanting through the AlN cap allows the highly disordered layer formation threshold fluence to be increased by one order of magnitude, as well as the annealing at high temperature (1300 • C) which brings about a strong optical activation of the rare earths.

Measuring strain caused by ion implantation in GaN

“…It has been suggested that strain is the driving force for defect transformation in GaN [17,18]. Strain, or more precisely the deformation perpendicular to the sample surface caused by implantation of a thin surface layer, can be directly measured via X-ray diffraction (XRD) which is very sensitive to small variations in the lattice parameter [21][22][23][24]. It was reported previously that the defect nature of extended defects caused by high fluence ion implantation is different in a-plane and c-plane GaN [25].…”

Electronic structure of ytterbium-implanted GaN at ambient and high pressure: experimental and crystal field studies

“…After implantation, the sample covered by GaN powder was annealed for 30 min at 700 • C, and then for 30 min at 1200 • C, each time with a nitrogen overpressure of 1 GPa. Such a procedure allowed for the use of higher annealing temperatures for better lattice damage recovery and optical activation of ytterbium while minimizing the risk of surface dissociation, the formation of nitrogen vacancies, and the diffusion of implanted ytterbium from inside the crystal to the crystal surface [19,[52][53][54][55][56]. Ion implantation followed by thermal annealing to recover implantation damage and to optically activate the RE 3+ ions is a common method of obtaining RE-doped GaN [8-11, 14, 15, 19, 20, 34-37, 45, 46, 56]; however, annealing with nitrogen overpressure is rarely done, mainly due to the lack of the unique equipment which is necessary to perform such a process.…”